This invention relates to batteries, and more particularly to rechargeable batteries.
DE 199 05 550 depicts a method for determining or indicating the charge state of a primary or secondary battery. Essentially, the battery is discharged so that only a minimum residual charge remains. The time required for the battery to be discharged (i.e., discharge time) is measured by a connected consumer measuring the time required for the battery voltage to drop to a first voltage threshold value, assuming the consumer has an essentially constant current consumption over an average time period. When the first voltage threshold value has been reached, it is reduced by an amount that depends on the discharge time measured. If the consumer further discharges the battery, so that the battery voltage drops still further, reaching the reduced voltage threshold value is an indicator for the discharge of the battery to a particular residual charge, i.e. for the presence of a low charge state of the battery.
DE 44 09 736 depicts a method and a device for caring for an accumulator (i.e., a rechargeable battery) incorporated in an accumulator-operated device wherein the memory effect is counteracted. In this known method, every few months the accumulator is automatically fully discharged and then fully recharged again. This accumulator care is only carried out if the accumulator-operated device is connected to the electrical outlet by means of a charging set, and if recharging after discharging is therefore certain. If the device is operated as described above, i.e. if the accumulator is always discharged for only a few minutes before being completely charged again, then accumulator care at shorter intervals would be desirable. On the other hand, accumulator care can be entirely done without if during operation of the device the accumulator is always first completely discharged before it is charged again.
The present invention includes methods and devices for the conditioning of a rechargeable battery in a manner reflecting the rechargeable battery""s state at the time the conditioning is performed.
Conditioning is intended to prevent as far as possible the changes in battery characteristics otherwise caused by ageing and by the memory effect.
In several aspects, the invention features a method of conditioning a rechargeable battery. In one aspect the invention features a method of conditioning a rechargeable battery, including providing a fully charged rechargeable battery and measuring a discharge time for which the voltage of the battery takes to decrease to a voltage threshold value. The discharge time is compared to a reference value, and if the discharge time is less than the reference value, the battery is shorted through a discharge load to further discharge the battery.
In the present application, discharge time does not refer to the time during which the battery voltage drops only as a result of self-discharge of the battery, but instead, discharge time refers to the time it takes for the battery to be discharged by way of a connected consumer, for example a device being operated by the consumer
In some embodiments, in addition to the discharge time, the current which flows during discharge is also measured, and from it, the charge quantity taken from the battery is determined. The charge quantity determined is compared with a comparison value, and if the battery voltage has dropped to the voltage threshold value before the charge quantity which corresponds to the comparison value has been taken from the battery, the battery is fully discharged.
In other embodiments, the time which has passed since the battery voltage last dropped to the voltage threshold value is also measured. If for example a device operated by the rechargeable battery is always used for a few minutes only before the battery is fully recharged again following use, the battery voltage is unlikely to drop to the voltage threshold value for some time. The same applies if, for an extended period, the device is not used at all or is seldom used. If this time exceeds a specified maximum time, in certain embodiments, the battery is discharged until the battery voltage drops to the voltage threshold value, and the discharge time which has passed since full load or battery change, or the charge quantity which has been taken since full load or battery change, is measured; the measured value is compared with the reference value or to the comparison value, and, if necessary, the battery is fully discharged. If in the case of exceeding the maximum period, the battery voltage is already below the voltage threshold value, the battery is fully discharged. Accordingly, the rechargeable battery is only fully discharged if this is necessary for maintaining the full service life of the battery, i.e. for getting rid of the memory effect. On the other hand, battery conditioning is not required if, during operation, the battery gets discharged frequently enough to the extent that the battery voltage drops below the voltage threshold value before the battery is charged again.
In another embodiment, the time is also measured which has passed since the battery was last charged or changed. If this time exceeds a minimum time and if during this time the battery voltage has dropped to the voltage threshold value as a result of self-discharge alone, then a display is activated which signals ageing, i.e. the need for a change of battery.
In another embodiment, the battery is recharged after discharge. In still another embodiment, directly after recharging, a complete battery conditioning cycle including complete discharge and subsequent recharge is performed. If the discharge time measured or the charge quantity taken is again below the reference value or comparison value, this indicates an aged battery. The display which signals the necessity for changing the battery is then activated.
This additional battery care cycle is preferably carried out by automatic discharge of the battery via a load resistor and automatic recharge. However, it can also be carried out by the user through normal operation of the device.
One aspect of the invention features an electrical appliance, which includes a discharge load and a rechargeable battery for powering the electrical appliance, which is connected through a switch to the discharge load and used for powering the discharge load. Additionally, the electrical appliance includes a connector for connecting the appliance to an external source of electrical energy, and an electronic circuit that discharges the rechargeable battery by shorting the rechargeable battery through the discharge load only while the appliance is connected to the external energy source.
In some embodiments, the electronic circuit measures a discharge time for which the voltage of the battery takes to decrease to a voltage threshold value, compares the discharge time to a reference value; and if the discharge time is less than the reference value, shorts the battery through the discharge load to further discharge the battery.
In some embodiments, the electronic circuit measures a current flow during discharge, determines a charge quantity from the measured current flow during the measured discharge time, compares the determined charge quantity with the charge quantity of a reference value, and if the battery voltage drops to the voltage threshold value before the charge quantity corresponding to the reference value is released, shorts the battery through the discharge load to further discharge the battery.
In some embodiments, shorting the battery through the discharge load fully discharges the battery.
In some embodiments, the current flow is measured while also measuring the discharge time.
In some embodiments, the electronic circuit measures a first time interval which has passed since the battery voltage last dropped to the voltage threshold value, determines whether the first time interval exceeds a maximum reference time, and if the first time interval exceeds the maximum reference time, shorts the battery through the discharge load to discharge the battery until the battery voltage drops to the voltage threshold value.
In some embodiments, the electronic circuit recharges the battery after shorting the rechargeable battery.
In some embodiments, the discharge load is a resistor disposed within the appliance.
In some embodiments, the electronic appliance is an electrical shaver or an electric toothbrush.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.